I got sound by going to control panel/Sounds and Audio/Speaker Settings, clicked the advanced option and changed my speaker from mono to stereo 5.1.
Also, if you have USB headphones, try another soundsource (speakers/headphones).
I have an onboard Realtek HD sound card. (Driver: Realtek High Definition Audio Vista 64bit Version R2.65)
When I start the game I'm only have sound in the Tripwire logo and the other manufacturer logos. If the menu is there is nothing more to hear.
No background music, no ingame sound, nothing!
Because nobody can lie on what could it mean?
I've been trying for days to solve the problem.
I had this exact same problem and running the UE3Redist.exe is what enabled sound for me.